Difference Between Sql Server VARCHAR and NVARCHAR Data Type

Below table lists out the major difference between the VARCHAR and NVARCHAR Data Type in Sql Server:

Sl. No.	Varchar[(n)]	NVarchar[(n)]
Basic Definition	Non-Unicode Variable Length character data type. Example: DECLARE @FirstName AS VARCHAR(50) =‘BASAVARAJ’ SELECT @FirstName	UNicode Variable Length character data type. It can store both non-Unicode and Unicode (i.e. Japanese, Korean etc) characters. Example: DECLARE @FirstName AS NVARCHAR(50)= ‘BASAVARAJ’ SELECT @FirstName
No. of Bytes required for each character	It takes 1 byte per character Example: DECLARE @FirstName AS VARCHAR(50) = ‘BASAVARAJ’ SELECT @FirstName AS FirstName, DATALENGTH(@FirstName) AS Length Result: FirstName Length BASAVARAJ 9	It takes 2 bytes per Unicode/Non-Unicode character. Example: DECLARE @FirstName AS NVARCHAR(50)= ‘BASAVARAJ’ SELECT @FirstName AS FirstName, DATALENGTH(@FirstName) AS Length Result: FirstName Length BASAVARAJ 18
Optional Parameter n range	Optional Parameter n value can be from 1 to 8000.Can store maximum 8000 Non-Unicode characters.	Optional Parameter n value can be from 1 to 4000.Can store maximum 4000 Unicode/Non-Unicode characters
If Optional Parameter n is not specified in the variable declaration or column definition	When this optional parameter n is not specified while using the CAST/CONVERT functions, then it is considered as 30.Example: DECLARE @firstName VARCHAR(35) = ‘BASAVARAJ PRABHU BIRADAR INDIA ASIA’ SELECT CAST(@firstName AS VARCHAR) FirstName, DATALENGTH(CAST(@firstName AS VARCHAR)) Length Result: FirstName Length BASAVARAJ PRABHU BIRADAR INDIA 30	When this optional parameter n is not specified while using the CAST CONVERT functions, then it is considered as 30.Example: DECLARE @firstName NVARCHAR(35) = ‘BASAVARAJ PRABHU BIRADAR INDIA ASIA’ SELECT CAST(@firstName AS NVARCHAR) FirstName, DATALENGTH(CAST(@firstName AS NVARCHAR)) Length Result: FirstName Length BASAVARAJ PRABHU BIRADAR INDIA 60
If Optional Parameter n is not specified in while using CAST/ CONVERT functions	Transactions are not allowed within functions.	Can use transactions within Stored procefures.
Which one to use	If we know that data to be stored in the column or variable doesn’t have any Unicode characters.	If we know that the data to be stored in the column or variable can have Unicode characters.
Storage Size	Takes no. of bytes equal to the no. of Characters entered plus two bytes extra for defining offset.	Takes no. of bytes equal to twice the no. of Characters entered plus two bytes extra for defining offset.

  As both of these are variable length datatypes, so irrespective of the length (i.e. optional parameter n value) defined in the variable declaration/column definition it will always take the no. of bytes required for the actual charcters stored. The value of n defines maximum no. of characters that can be stored.